Many powders, especially with viscoelastic compaction mechanism, such as
starch or avicel, exhibit large degree of stress relaxation (with time
dependent deformation).

If you monitor punch
displacement and compression force, you can make pretty accurate assessment of
the compactability of your material. If LVDTs are attached to both upper and
lower punch, it is possible to actually measure in-die thickness of the tablet
at various compression levels. On this plot you can see how the tablet
thickness rapidly decreases in the compression stage and then gains some
thickness during the decompression stage of the tableting cycle. The
degree of this increase in thickness is indicative of the elastic recovery as
the pressure is removed from the tablet.